1. Field the Invention
The present invention relates to a display apparatus adapted for a display wall, an image adjustment method therefor and a display wall therewith, specifically to a digital display apparatus adapted for a display wail, an image adjustment method and a display wall therewith.
2. Descriptions of the Related Art
In recent years, display walls were popularly used in occasions with large-scale displays. The display wall is arranged by combining several display apparatuses together. Each display apparatus selects a part of image according to the corresponding arranged position and scales to a full-screen size of the display apparatus. All the combined display apparatuses therefore jointly display a whole image of the input signal.
FIG. 1 is a diagram of a display wall consisting of 3×3 display apparatuses. In FIG. 1, 100 is a video source and 111, 112, 113, 121, 122, 123, 131, 132 and 133 are nine display apparatuses which are combined into a 3×3 display wall. A video signal of the video source 100 is connected individually to each display apparatus in an order of signal lines 140, 141, 142, 143, 144, 145, 146, 147 and 148 to transmit the video signal in cascade to all of the display apparatuses through the signal lines in serial. Each cascaded display apparatus selects a corresponding part of the image according to the arranged position and scales the selected part to display. The scaled displays are therefore jointly combined into an enlarged one of the original image.
Due to the features of clearness, sharpness and lossless in transmission of a digital display technique as compared with traditional analog display techniques, digital display elements (such as LCD, PDP, DMD) have replaced traditional analog display elements gradually to become a new generation of display apparatuses in recent years. For CRT-based display apparatuses, both size and position of an output image can be controlled by adjusting a horizontal deflection and a vertical deflection. For those digital displays of new generation, a scaler is usually equipped internally for image scaling and frame rate conversion. The adjustment of the image size and display position can be achieved by controlling a scaling factor of the scaler and an initial image capture position for an input image respectively.
The prior art display techniques relating to digital scaling provide a set of preset scaling modes (such as scaling to a full-screen of the display apparatus, maintaining a fill aspect ratio, maintaining a native-resolution) for users to select one of the scaling modes to set the scaling factor of the display apparatus. The preset scaling modes are not suitable for adjusting image for individual display apparatus used in the display wall. This is because that in the application of display walls individual display apparatus may fine-tune its scaling factor and position according to corresponding arranged position to combine individually displayed image into a whole continuous and complete image.
In order to achieve the image continuity between each two adjacent display apparatuses, the position of the input image is adjusted usually in the past. A drawback in such way is that a precision degree to adjust the output image relates to the current scaling factor of the image.
For example, one pixel movement of a pixel in the input image is enlarged to a two-pixel movement of the horizontal signal of the output image if an image has been enlarged into two times in horizontal. Consequently, the adjustment method cannot keep continuity of the displayed image between neighbored display apparatuses. The major image discontinuity is due to the image scaling problem in multiplication of fraction numbers. Taking a 3×3 display wall as an example, if a display screen with an XGA (Extended Graphics Array) resolution (i.e., 1024×768) is scaled to a display wall with 3×3 display apparatuses, the horizontal input signal should be averagely divided into 1024/3=341.3. However, the minimum unit for the input image is one pixel in a digital image system. Consequently, choosing 341 pixels for scaling results in a shortage of some part of the displayed image; choosing 342 pixels for scaling results in a replication of some part of the displayed image. These lead to the image discontinuity between neighbored display apparatuses among the display wall.
The prior art applications about the digital scaling display provide sets of scaling modes such as scaling to a fill-all screen of the display apparatus, maintaining a fill aspect ratio, maintaining native-resolution, etc. For a convenient understanding, please refer to FIG. 3A to FIG. 3D as an example. In FIG. 3A, an image 310 is a captured image with a 720×400 resolution. The desired output resolution of the display apparatus is 1024×768, for example. If a scaling mode is scaling to a fill-all screen of the display apparatus, the output screen is shown as a display screen 320 in FIG. 3B that the scaled screen fills the whole display apparatus. However, the difference between horizontal and vertical scaling aspect ratios of the image will cause the loss in maintaining horizontal and vertical aspect ratio of the image to be displayed.
If a scaling mode is scaling with maintaining a fill aspect ratio, the output screen is shown as a display screen 330 in FIG. 3C that maintains the horizontal and vertical aspect ratio of the original screen. However, each top and bottom side of the display screen leaves an empty area of 1024×100 approximately. If a scaling mode is scaling with maintaining native-resolution, the output screen is shown as a display screen 340 in FIG. 3D that maintains the original display resolution (i.e., 720×400). However, an empty area is left in the surrounding area of the display screen. Users can select one of the said scaling modes depending on the usage conditions or preferences. However, the preset scaling modes cannot be applied for the display wall applications. While combining multiple display apparatuses to display an image, sometimes the scaling factor must be fine-tuned with the precision degree of a pixel in horizontal or a line in vertical to combine the image display areas perfectly and completely.